Conventionally, various patterns of improvements have been made regarding a scheme, e.g., HSDPA (High Speed Downlink Packet Access), which allows high speed packet transmission on the downlink from a wireless base station to a communication terminal. This is associated with a need for an expansion which allows data transmission of a large capacity or low latency also on the uplink from a wireless base station to a communication terminal, and the standardization of high speed packet transmission is currently considered by 3GPP.
Also in the high speed packet transmission on the uplink, like on the downlink, a study for introduction of a scheduling technique is ongoing. Uplink packet scheduling is carried out in a base station and the base station transmits the prepared scheduling information to each communication terminal. Each communication terminal transmits an uplink packet to the base station based on the scheduling information received from the base station. Moreover, in scheduling in the base station, a communication terminal which is allowed to transmit an uplink packet is selected, and, to this selected communication terminal, communication parameters such as allowed transmission rate and transmission power are transmitted on a downlink control signal.
One of the scheduling methods in high speed packet transmission on the uplink is a method called “Time and rate scheduling” (see non-patent document 1). This “time and rate scheduling” includes the following three steps. That is, in the first step, a communication terminal reports a transmission rate request, data amount, transmission power margin and so on to a base station. Next, in the second step, the base station carries out scheduling based on the reported transmission rate request, data amount, transmission power margin and so on, and selects a communication terminal which is allowed to transmit an uplink packet, and, to this selected communication terminal, communication parameters such as allowed transmission rate and transmission power, are indicated on a downlink control signal. Then, in the third step, the communication terminal, which received a control signal addressed to the communication terminal, transmits an uplink packet at a transmission rate lower than the transmission rate indicated by the base station or with a transmission power lower than the transmission power indicated by the base station.
Here, as the transmission rate which is available for high speed packet transmission on the uplink, 32 patterns of MCS's (Modulation and Coding Scheme) are proposed in “3GPP, R1-030667, HARQ Efficiency in E-DPDCH” (non-patent document 2). Moreover, with regard to the transmission of a control signal on the downlink when using these MCS's in time and rate scheduling, a proposal is made in “3GPP, R1-031232, Text Proposal on DL Signaling Overhead” (non-patent document 3). In non-patent document 3, “5-bit reconfiguration pointer” is proposed as “E-DCH TFCS reconfiguration” (i.e., scheduling Grant for Time-and-Rate scheduling). Because 32 patterns can be represented with five bits, non-patent document 3 proposes that 32 patterns of control signals capable of indicating all the 32 patterns of MCS's to a communication terminal are prepared in advance.    Non-Patent Document 1: 3 GPP, R1-030592, Node B Controlled Time and Rate Scheduling    Non-Patent Document 2: 3 GPP, R1-030667, HARQ Efficiency in E-DPDCH    Non-Patent Document 3: 3 GPP, R1-031232, Text Proposal on DL Signaling Overhead